In the context of two projects, one funded by the German Federal Ministry for
Education and Research (BMBF) and the other organised by the Federal Waterways
Engineering and Research Institute (BAW) and the Federal Institute of
Hydrology (BFG), extensive surveys and field experiments on morphology,
hydraulics and sedimentation were carried out in groyne fields in the lower
middle Elbe between Sandau and Wittenberge from 1997 to 2002, taking into
account the extreme flooding in August 2002. The data were analysed in
Geographical Information Systems and changes were quantified over certain time
periods. The aim was to differentiate between the influence of hydraulic
engineering as a factor of various groyne types (on the micro scale) and the
influence of particular river areas (meso to macro scale). Digital terrain
models were employed, for example to determine the bank contours with varying
water levels and the thickness of sedimentation in the groyne fields. The
thickness of sedimentation varied as a factor of the particle distribution in
the talweg and is thus primarily dependent on the section of the river, i.e.
influenced by meso and macro scale effects. The type of accumulation within
the groyne fields (micro level) is modified by the groynes. Extensive
measurements of the hydraulic conditions in groyne fields were carried out at
low and high water levels. The proportions of flow speeds at different water
levels were quantified and were also used to calculate shear stress. No
differences determined by the river areas examined could be found as for the
extent of sedimentation and the grain size distribution. The slight
differences between the groyne fields are influenced more by the location of
the groyne fields and the structure of the groynes. Furthermore, the links
between periodic fluctuations in water level and regular changes in flow in
groyne fields for groynes that are not submerged was studied in more detail on
the basis of field experiments. In two different groyne fields regular
oscillations of flows and water levels were identified with a periodicity of
c. 4 to 5 minutes and recognised laboratory results on this phenomenon were
confirmed. The possible impact of river navigation was taken into account and
did not play a role in this context. Repeated measurements at groyne fields in
various sections of the river made it possible to calculate bathymetry changes
and thus to calculate sediment inputs and/or outputs after individual phases
and after several phases. In particular the aggregated results from 2001 to
2002 including a low water phase, a biannual winter flood and the extreme
summer flood event revealed a differentiation in river sections that
corresponded to the categorisation on the basis of long-term sediment
thickness. Irrespective of the summer flood in 2002, a once-in-fifty years
event, an ongoing tendency to sediment accumulation was identified. A further
key aspect was the link established between flow speeds, morphologies and
substrata on the one hand and habitat preferences of various groups of fauna
in order to calculate habitat suitability. Such studies were carried out
taking selected fish, ground beetles and macro-zoobenthos as examples and made
it possible to identify the spatial distribution of micro to meso-scale
parameters that give rise to differing species spectrums in the areas studied.